The present invention relates to a method of producing a shaped article of a rigid aromatic heterocyclic copolymer having excellent heat resistance, mechanical properties, chemical resistance, electric properties, etc., as well as high elongation and high bending strength.
It is known that polymers containing heterocyclic repeating units such as thiazole rings, imidazole rings, oxazole rings, oxazinone rings etc., have a high rigidity and excellent mechanical strength, tensile modulus, heat resistance, etc. Therefore, it is expected that these polymers are used as plastic substitutes for metal materials alone or in combination with other engineering plastics.
However, the rigid aromatic polymer such as the aromatic polythiazole generally has a poor solubility in organic solvents, etc. due to its high rigidity, and it is soluble only in limited kinds of strong acids such as methane sulfonic acid, chlorosulfonic acid, etc. Also, it has only poor elongation and flexibility, meaning that it is poor in moldability. Accordingly, it is difficult to mold the rigid aromatic polymer without mixing with other materials.
Also, even in the case of forming a composite material of the rigid aromatic polymer and a matrix polymer, the above problem of poor moldability still remains. Further, since the rigid aromatic polymer does not show a good compatibility with the matrix polymer, it is difficult to blend the rigid aromatic polymer with the matrix polymer at a desired proportion.
To overcome such problems, it is possible to introduce a flexible moiety into the rigid aromatic polymer, thereby improving the moldability of the rigid aromatic polymer. Also, to improve the compatibility of the rigid aromatic polymer with the other polymer, it is possible to introduce a moiety compatible with the other polymer, which has the same structure as or a similar structure to the repeating unit of the other polymer, into the rigid aromatic polymer.
One example of such an attempt is disclosed by Japanese Patent Laid-Open No. 63-256622, which is a method of producing an aromatic heterocyclic copolymer by reacting a particular aromatic oligomer having a thiazole ring with a monomer having a benzene ring provided with at least one carboxyl group and at least one amino group in a polyphosphoric acid. The aromatic heterocyclic block copolymers obtained by this method have rigid molecular chain moieties and soft chain moieties.
However, in the above method, the synthesis of the aromatic heterocyclic copolymer is conducted while being heated in a polyphosphoric acid. Also, when the aromatic heterocyclic copolymer obtained by this method is combined as a reinforcing material with another polymer to provide a molecular composite material, the aromatic heterocyclic copolymer does not show a high compatibility with the matrix polymer because it already has a rigid molecular chain moiety such as a thiazole ring. Therefore, the aromatic heterocyclic copolymer obtained by the method of Japanese Patent Laid-Open No. 63-256622 is not suitable for use in a molecular composite material. Furthermore, Japanese Patent Laid-Open No. 63-256622 does not disclose a method of forming a shaped article of the aromatic heterocyclic copolymer.